I created a dish about 8 years ago when me and my husband were living on about 800 a month and had a baby. We call it chicken and rice.
You cook up chicken, cut it into pieces, the poorer you are the less chicken you get. Rice, steamed. Frozen veggies, usually carrots, cauloflower, and broccoli mix but you can use whatever. Heat up the veggies, chop them into smaller pieces.
Combine all three, add either a can of cream soup (any flavor you like, fat free works good too if you're trying to watch your waist line) or add teriaki. It helps mix it up.
Another fairly cheap dish is you cook up either a pound of hamburger or sausage, drain it. Chop up some potatoes small little chunks, scramble some eggs, combine. My kids love it. We don't have a name for it, but I had it growing up.
Also if you're poor avoid a lot of pre-made stuff, making your own stuff does cut down on expense while raising the quality of what you're eating.
Frozen veggies are a great way to pack in those veggies into your meals without paying a lot for them.
Also smoothies can be fairly inexpensive.
I use juice, milk, and fresh/frozen fruit. A cup of fruit, 1/4 cup juice 1/4 cup milk make some amazing smoothies, make any combination you want, but use a strong juice. Avoid overripe bananas unless you're making a banana smoothie as they have a tendancy to take over, so be careful with how much you use. If it's too tart a little bit of sugar can be added. Also yogurt can be added as well, I use low-fat vanilla, it adds a great flavor and texture.